Preheat oven to 350 degrees F. Prepare an 8-inch x 8-inch baking pan with non-stick baking spray.
Add 1½ cups flour, 1 cup sugar, ½ teaspoon salt, 1 teaspoon baking soda and 3 tablespoons cocoa powder to a medium bowl. Whisk to combine.
Create a well in the middle of the dry mixture and add in 1 tablespoon vinegar, ½ cup vegetable oil, 1 teaspoon vanilla and 1 cup hot water.Stir until the mix is just combined.
Pour batter into prepared baking pan. Bake for 30 to 35 minutes, or until a toothpick comes out clean. Let the cake rest, until cool.
Meanwhile, make the glaze by adding 2 cups powdered sugar, 3 tablespoons cocoa powder, ¼ cup water, 1 teaspoon vanilla extract and a pinch of salt to a bowl. Whisk together until a shiny glaze is formed and no lumps are present.
Pour the glaze over the cooled cake and use the back of a spatula to spread evenly. Let rest until glaze is set. Slice and enjoy!